Sodium, calcium, lithium alloy hydrofuel



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April 4, 1961 R. B. cox 2,978,304

SODIUM, CALCIUM, LITHIUM ALLOY HYDROFUEL Filed July 5, 1952 MELTING POINT CURVE OF LITHIUM-CALCIUM ALLOY (X: ALLOY 5% SODIUM) PERCENTAGE OF CALCIUM BY WEIGHT IN V EN TOR.

BIYQKLH-LB' CD74 United States Patent r 7 12,978,304 s 7 SODIUM,"CALCIUM,LIT HIUM*ALLOY.

HYDROFUEL Robert B. Cox, Pomona, Calif., assignor, by mesne assignments, to Aerojet-General Corporation, Cincinnati, Ohio, a corporation of Ohio Filed July '5, 1952, Ser. N5. 297,380

2 Claims. c1. sz .s

fuel that has a high energy content both per unit weight and per unit volume of the material.

Of all of the pure metals which have been found suitable as hydrofuels, only metallic lithium has a sufliciently low melting point combined with an energy content which is high enough to be of any practical value. Lithium metal, however, is scarce and costly and its melting point while lower than that of most water-reactive metals, is still high enough to make it difficult to use in some types of underwater equipment. A

In accordance with the present invention I have discovereda suitable lithium-base alloy which melts at a much lower temperature than metallic lithium, possesses a high energy content both per unit volume and per unit weight, is relatively low in cost, can be handled reasonably safely, and can be utilized in many underwater jet propulsion devices.

The hydrofuel according to my invention comprises essentially an alloy of lithium with calcium. This alloy, by test, has an energy content per unit weight comparable to that of lithium and higher than that of lithium per unit volume and melts at a temperature well belowthe temperature at which pure lithium becomes fluid.

The melting point for commercial lithium is 359 ing point curve for lithium-calcium alloys, between 0 and 50% calcium, isgiven in the accompanying drawing in the curve designated by O-OO--.

Referring to the drawing, it can be seen that the temperature, at which the binary alloy melts, gradually decreases from 0% calcium up to about 32% calcium. Beyond this point the melting point curve becomes substantially constant until the percentage of calcium in the alloy reaches 46% by Weight. Through this range of from 32 to 46% by weight calcium, the melting point of the binary alloy is reasonably low and at 46% calcium it reaches its lowest point. Above 46% by weight of calcium, the melting point curve rises sharply and by the time the mixture has reached 50% by weight calcium the melting point is almost as high as the melting point of lithium metal.

Between the range of 32 and 46% by weight of calcium, the melting point of the calcium-lithium alloy varies between 292 and 295 F. This is an appreciable reduction from the 359 F. melting point of lithium and is low enough to permit the use of the alloy as a V 2,978,304 l atented Apr. 4,

ICE

.molten liquid alloy heated even as high as 325 F. does not possess the most satisfactory ignition properties upon injection into water. It is commonly desired of a hydrofuel that the substance ignite readily on coming in contact with water. In fact it is desirable that the reaction should begin to take place immediately and spontaneously on contact with water and preferably with substantially explosive rapidity.

I have found that the desired rapid rate of reaction on contact with water can be achieved in alloys of lithium and calcium containing as much as 32 to 46% by weight calcium by adding to the alloy from 2% to 5% by weight of metallic sodium.

Although the presence of the sodium aids the ignition, it does not have any harmful or very great effect on the melting point. Actually the presence of the sodium somewhat lowers the melting point below that of the lithium-calcium alloy alone.

It has been determined that when the percentage of sodium in the alloy is less than 2% by weight based on the weight of the mixture, the sodium content in the mixture is too low for good spontaneous and explosive ignition in water when the molten alloy is injected therein. It has furthermore been found that an excess of about 5% sodium will not alloy and therefore becomes ineffective. The melting point of the ternary alloy of lithium with from 30 to 44% calcium and 5% by weight sodium exhibits a melting point ranging from 285 to 286 F. According to the curve marked XXX this appears to take place when 53% parts by weight of lithium are alloyed with 41 /2 parts by weight of calcium to which has been added 5 parts by weight of sodium.

Since calcium is cheaper and more available than lithium, and because of the increased density achieved by adding an element having a higher specific gravity than lithium, the preferred alloy should contain as much calcium as possible.

A way in which this alloy can be compounded is as follows: The required amount of lithium, calcium and sodium are introduced into a melting pot in which an inert atmosphere is present such as for example, helium, argon, neon, etc. The pot is then heated to between 500 and 600 F. and maintained at this temperature until all of the ingredients have melted to form the threecomponent alloy. Even though the melting point of calcium is 1490" F., the melting point of lithium is 359 F., and the melting point of sodium is 208 F., the molten mixture of sodium and lithium when heated to between 500 and 600 F. dissolves the higher melting calcium. As soon as the alloy is formed, it is cast in a mold, allowed to cool and stored under air tight anhydrous conditions making it ready for use in underwater jet propulsion motors.

The alloy may be stored by packing and sealing the cast grains in water proof airtight containers, or by storing the alloys under pure white mineral oil in which case the containers do not have to be air tight.

. v 3 from about 3 0% to v about 44% by Weight of ca m, and from about 51% to about 68% by weight of lithium.

References Cited inthe file of this patent I UNITED ,SIAIE BA ENI 515,500 :Nohel Feb-.27, '1894 1,532,930 O?Neil l Apr. '7, 1925 2,573,471 Malina et a1. Oct. 30, 1951 4- OTHER REFERENCES Bielkowicz: Evolution of Energy in Jet and Rocket Propulsion, Aircraft Engineering, vol. 18, No. 205, March 1946, pp. 90-92.

Journal of the American Rocket Society, No. 72, December 1947, pp. 10, 14-22 inclusive.

Grant: Lithium as 2 Suggested Rocket Fuel, The Journal of Space Flight, vol. 2, No. 10, December 1950, pp. 3-5 inclusive. 

2. A NEW HYDROFUEL COMPRISING A TERNARY ALLOY CONSISTING OF FROM ABOUT 2% TO 5% BY WEIGHT OF SODIUM, 